After slacking for a week or so, I got it stripped down and upon closer inspection it was the tubes that were too thin which was causing the problem. They were measuring in at 24.7mm and there was alot of play in the Z tubes, X and Y we’re not so bad and some play in those as well.
So, armed with my calipers I took a road trip to a metal shop and came back with some 25.2mm thick walled aluminium seamless tube for a grand total of £20 cut to length. now it fits really snug, all bearings in contact and much much stiffer.
For any UK guys interested I went to Forward Metals in B’ham, they also have an ebay shop, and the guy Tim will now know what your talking about if you want to talk MPCNC tubes with him.